1. Field of the Invention
This invention relates to a process for treating waste water discharged during a painting process in a machine manufacturing factory (i.e., waste water containing a resin, pigment, etc.), or waste water discharged from various equipment in such a factory, containing organic matter and including the waste water mentioned above.
2. Description of the Related Art
Waste water containing organic matters is discharged in a large quantity from various equipment in a factory manufacturing machines, such as automobiles, (for example, waste water from a pit for circulating water from one painting booth to another, waste water produced by a shower test conducted to ascertain a tight seal on an assembly, waste water from a mess room and waste water from a water purifying tank). A painting plant, among others, discharges a large quantity of water circulating in a pit from one booth to another during a painting process, and such waste water contains a large amount of resins and pigments originating from a mist of paint. Waste water containing organic matter, such as a synthetic resin, has hitherto been treated for its separation by flocculation and flotation.
For treating such waste water, there has been employed a process which includes adding an inorganic flocculant, such as polyaluminum chloride, aluminum sulfate or ferrous chloride, to a waste liquid to cause it to undergo a flocculation, adding a polymeric flocculant, such as poly(meth)acrylamide or poly(meth)acrylic acid, to the flocculated waste liquid to form flocs (cotton-like flocculated masses), and separating them by flotation.
The above process using an inorganic flocculant has the drawback that the amount of the sludge produced by the treatment of waste water drastically increases as the amount used of the flocculant.
In order to overcome the above-described drawback, Japanese Patent Laid-Open No. 75703/1995, for example, describes a process which includes adding a silica type flocculant (a solution of blast furnace slag in dilute hydrochloric acid) to waste water containing an emulsion, etc. to grow a precipitate, and removing oily matter by flotation under pressure.
Japanese Patent Laid-Open No. 111407/1990 describes a process which includes adding a composition obtained by mixing a CaO--MgO--SiO.sub.2 compound and a metal salt comprising an iron salt or a magnesium salt to a waste liquid containing an emulsion to flocculate resin particles in the liquid, and separating the flocculated particles.
Although these processes using inorganic flocculants have made it possible to reduce, as compared with the related art process, the amount of the sludge to be thrown away, its reduction is still unsatisfactory, and a further reduction thereof is desired. Moreover, the inorganic flocculants necessitate a complicated process for preparation, and are, therefore, too costly to be suitable for use on an industrial basis.